This invention relates to a throw away cutter in which the runout of cutter edges is minimized and the number of cutter edges can be increased by improving the shape of chip pockets formed in the cutter.
In recent years, throw away cutters having a high-rake structure for higher cutting ability are increasing in number partly because of an increasing difficulty in cutting materials to be cut and partly because of the increasing requirement for accuracy.
But with many of these cutters, the chip pockets formed in the body for the respective cutter edges are still the same chip pockets that have been used conventionally. Namely, as shown in FIG. 7, they are in the shape of through grooves having a cylindrical wall. In the figure, 1 is a cutter body, 2 is a throw away insert having a cutting edge 2a, and 3' is a chip pocket.
As shown in FIG. 8, such conventional chip pockets 3' are formed by thrusting a rotating spherical machining tool A such as a ball end mill through the cutter body in the direction of an arrow in FIG. 7. The surface of the pocket thus formed has a uniform radius of curvature and extends obliquely rearwardly from the front of the body toward the outer periphery along the cutting edge.
Since chips tend to flow along the rake face, if the cutting edges are of a high rake type, there is no need to form large pockets at the front or inner side. Rather, in order to achieve high performance, it will be more important to increase the rigidity of the body by reducing the pocket size at the front or inner side.
But since conventional chip pockets are in the form of through grooves having a uniform radius of curvature, the higher the rake angle of the cutter edges, the more the cutter body has its front side cut off more than necessary. This results in a back metal portion 1a for supporting the inserts which is too thin to assure the rigidity of the body. This will in turn worsen the runout of the cutter. If the thickness of the back metal portion 1a were increased, the total number of cutting inserts would have to be reduced. This will have a bad influence on the working efficiency and the accuracy of working surface.